From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41693C433F5 for ; Thu, 24 Feb 2022 13:15:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234186AbiBXNQC (ORCPT ); Thu, 24 Feb 2022 08:16:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231145AbiBXNP7 (ORCPT ); Thu, 24 Feb 2022 08:15:59 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3CF65166E11 for ; Thu, 24 Feb 2022 05:15:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645708528; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=R0lJYwvTZOZVdJ4O7bKhvvzTAAdIE1Ye5K2uSbURukI=; b=bK//y7ovI88mp2+dbJg9l4vs9ciBlyCa4LCtA8EJ3yOe5/DYSSiVx4uDYpv4PPbWqBFIQk k+R5EfHQrLy66cnTyoWsrdvxyVTu0JPnOtgvBZxkCv5+Py6ymX11Hj6dPvxgwn8epgO/cW ea566Q8Y+4LSZmpekhu87fmW+L6kPo0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-643-E3FskdubMYSN1vTPcI5-nA-1; Thu, 24 Feb 2022 08:15:23 -0500 X-MC-Unique: E3FskdubMYSN1vTPcI5-nA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E2F5B1854E21; Thu, 24 Feb 2022 13:15:21 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8936310631F7; Thu, 24 Feb 2022 13:15:19 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id D8300416D862; Thu, 24 Feb 2022 10:14:58 -0300 (-03) Date: Thu, 24 Feb 2022 10:14:58 -0300 From: Marcelo Tosatti To: Aaron Tomlin Cc: Frederic Weisbecker , Christoph Lameter , tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Phil Auld Subject: Re: [RFC PATCH] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: References: <20220203214339.1889971-1-atomlin@redhat.com> <20220217124729.GA743618@lothringen> <20220217142615.xqtiydixvnumyvei@ava.usersys.com> <20220217163205.GA748087@lothringen> <20220218125454.utlgmuhijklzr3if@ava.usersys.com> <20220219154616.pwsvh445x3vn7ltf@ava.usersys.com> <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220224130014.rmhtx3xlepybuxn2@ava.usersys.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 24, 2022 at 01:00:14PM +0000, Aaron Tomlin wrote: > On Thu 2022-02-24 09:27 -0300, Marcelo Tosatti wrote: > > But Aaron, vmstat_shepherd should be ensuring that per-CPU vmstat_update > > work are queued, if the per-CPU vmstat are out of sync. > > Hi Marcelo, > > Yes, I agree; albeit, as far as I understand, in the context of a nohz_full > CPU that has its scheduling-clock tick stopped, we cannot rely on any > deferred work. > > The purpose of my patch was to prevent a nohz_full CPU from entering idle > state when CPU-specific vmstat data is non-zero. > > > And: > > > > static void > > trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) > > { > > if (!is_timers_nohz_active()) > > return; > > > > /* > > * TODO: This wants some optimizing similar to the code below, but we > > * will do that when we switch from push to pull for deferrable timers. > > */ > > if (timer->flags & TIMER_DEFERRABLE) { > > if (tick_nohz_full_cpu(base->cpu)) > > wake_up_nohz_cpu(base->cpu); > > return; > > } > > > > * @TIMER_DEFERRABLE: A deferrable timer will work normally when the > > * system is busy, but will not cause a CPU to come out of idle just > > * to service it; instead, the timer will be serviced when the CPU > > * eventually wakes up with a subsequent non-deferrable timer. > > > > You'd want that vmstat_update to execute regardless of whether there are > > armed non-deferrable timers. > > > > Should fix both 1 and 2 AFAICS. > > > > If I understand correctly, you are suggesting to switch to a non-deferred > timer for such work when the scheduling-clock tick is stopped? Indeed, it > would address both scenarios yet I'm not sure we'd want that due to the > performance impact which might be more than negligible. Aaron, If the per-CPU vmstat_update is limited to happen once per second, that shouldnt be a significant performance impact?